Yesterday, EPA released proposed revisions to its rules governing emissions from emergency back-up generators. It’s not always the most exciting of topics, but it is important. Many facilities have back-up generators and I know from experience advising clients that, precisely because back-up generators do not run that often, operators can run into compliance issues.

The most important aspect of the proposed rule is that EPA would allow back-up generators to run for up to 100 hours without being subject to emissions limits for the following reasons:

Monitoring and testing

Demand response

Voltage changes of at least 5%

Moreover, EPA is proposing that, through 2017, emergency generators be allowed to operate without limits for up to 50 hours of this 100-hour exception “for peak shaving and non-emergency demand response.” EPA’s explanation is that this temporary exception is necessary “to address reliability issues and develop solutions to reliability issues while facilities are coming into compliance with the” utility MACT rule.

I find it interesting that, according to the Daily Environment Report, the Electric Power Supply Association opposes the rule. EPSA President John Shelk was quoted as commenting that:

The essential design and purpose of demand response is to encourage consumers to reduce their consumption of electricity in response to appropriate market signals, not to simply replace power from the grid with power from an on-site emergency diesel generator not subject to the same air emissions rules.

This is actually something of a difficult issue. Back-up generators are an important element of flexibility in grid operations. On the other hand, EPSA makes a fair point that one does not typically think of utilization of back-up generators as a component of “demand response”.

Indeed, one could fairly think of use of back-up generators as a “supply response.”